When the controversy over the price of the EpiPen exploded late last summer, many consumers asked why there was no substitutable generic version available.

The answer was complex: while the key ingredient in the anaphylaxis treatment, epinephrine, has been available for decades and is no longer covered by a patent, the delivery device proved hard for generic competitors to copy to a degree that would satisfy regulators.

The FDA guidance says that generic copies with some design differences may be approved as substitutable products, as long as those differences don't affect patients' ability to use the product the way it's intended.

"Those design differences might correlate with different instructions for use of the two products," the agency's commissioner, Dr. Scott Gottlieb, said in remarks at the FDA published Tuesday morning.

"Under this guidance, so long as the generic applicant is able to demonstrate with data, where appropriate, that differences in design of the generic product do not affect the clinical effect or safety profile when the generic is substituted for the branded product, the generic product can be approved as a competitor to the branded drug where all other requirements for generic approval are met," Gottlieb said.

The agency is also seeking to clarify guidelines on what constitutes "sameness" between generic and branded medicines.

The FDA didn't mention any drug or therapeutic class by name, referring to a category of complex generics that includes medicines delivered through devices like metered dose inhalers, or auto-injectors.

The move comes as Gottlieb has acted on President Donald Trump's directive to bring drug prices down, mainly by increasing generic competition.

There are other epinephrine auto-injectors already on the market competing with the EpiPen, which is made by Mylan, such as Impax Labs' Adrenaclick. None have the dominance or name recognition of the EpiPen, and cannot be directly substituted at pharmacies when doctors write prescriptions for EpiPens.

Teva had sought to bring a direct generic competitor to the EpiPen to market, but said in early 2016 that its product was rejected by the FDA for "certain major deficiencies."

In response to criticism over the price of the EpiPen, Mylan introduced its own generic version at half the price. It's an identical version of the product without the same branding.

Gottlieb said the goal of the new guidance "is to promote generic entry as a way to foster price competition, and improve access to healthcare."

The FDA, he said, has "committed to put out guidance laying out how a generic firm would copy a particular complex drug at least two years in advance of the first potential generic entrant."